Heretofore, for glass plates and transparent resin plates for windowpanes, wall surfaces, partitions, or for illuminations to be used in space exposed to black light irradiation, a color sheet has been proposed for use for light transmission control. However, use of such a color sheet, as stuck to windowpanes of ordinary constructions, involves a problem in that the quantity of external light that would pass through the sheet in rainy or cloudy days or during evening hours is small and therefore sufficient brightness could not be secured inside the constructions.
Recently, for solving the problem, a color sheet using a photochromic dye has been proposed (see PTL 1 to 4). The photochromic dye reversibly changes the color thereof depending on light irradiation. In other words, the dye has a characteristic of such that it colors when irradiated with sunlight or UV rays such as black light or the like, but on the other hand, it gets back to be colorless in the environment not exposed to UV rays.
The color sheet disclosed in PTL 1 to 4 uses a photochromic dye having such a characteristic, and therefore it is said that the sheet can block light in the environment exposed to UV rays, but is transparent in the other environments.